1. Field of the Invention
The present invention relates to a polarizing film. A polarizing film of the present invention independently or a laminating optical film may form a visual display, such as a liquid crystal display, an organic EL display, a PDP (plasma display panel) a liquid crystal display.
2. Description of the Prior Art
In a liquid crystal display, it is indispensable that polarizers should be arranged at both sides of a glass substrate that forms a top surface of a liquid crystal panel according to a picture formation method. Generally, polarizing film is used a polarizer, comprising a polyvinyl alcohol derived film, and dichroism substances, such as iodine, on which a protection film is adhered.
Conventionally, the above described polarizing film is manufactured by adhering a polarizer and a protection film by adhesives. Adhesives are compounds or composites that have combining components, and are used also as solution dissolved in water or organic solvents. Furthermore, they are hardened with heat, light irradiation or by a chemical reaction, etc. Such adhesives are poured in between these layers, immediately before the polarizer and the protection film are adhered, or they are beforehand applied to either of the polarizer or the protection film.
However, when adhesives are used, many processes are needed in manufacturing process and then a large amount of expense is required in production facilities in which an application process, a laminating process and a drying process of adhesives are required. Further a saponification processing, a corona treatment, a plasma treatment, a low-pressure UV processing or an undercoat processing etc. should be given to a protection film, in order to raise an adhesive property with a polarizer. Consequently, production cost of the polarizing film obtained also becomes expensive. Moreover,if the manufacturing process requires many steps, a factor of giving defects in each of the process will also be increased.
Moreover, as the above-mentioned adhesives, many water-soluble adhesives, such as polyvinyl alcohol aqueous solution, are used, and then a produced polarizing film does not have sufficient durability under a heated or humidified condition. Therefore, the portion of adhesives is easy to be influenced with moisture, and this is one of the causes of degradation of a polarizing film in early stage of use.